1. Field of the Invention
This invention relates to a process of producing a nonwoven web from a primary nonwoven web, which is disintegrated into individual fibers and is then caused to form a fibrous covering on a rotating drum and is subsequently caused to form at least one stream of fibers, which in an entraining air stream is applied to a continuously moving collecting surface, through which the entraining air stream is sucked off, and to an apparatus for carrying out the process.
2. Description of the Prior Art
In order to produce a nonwoven web from a primary nonwoven web it is known (U.S. Pat. No. 3,641,628) to feed the primary nonwoven web via a feeding trough to a carding drum, by which said web is disintegrated into individual fibers and which cooperates with pairs of worker and clearer rollers to equalize said individual fibers, whereafter the covering composed of the individual fibers is separated from said drum by the action of centrifugal force and by the action of an entraining air stream which is tangential to the carding drum. In order to form the nonwoven web the individual fibers are deposited on a collecting surface, which is disposed below the carding drum and is continuously moved and the entraining air stream is sucked through said collecting surface. Whereas the carding operation and the equalization of the dissolved nonwoven web by the pairs of worker and clearer rollers can be performed so that a substantially uniform covering composed of individual fibers is prepared at the point where the fibers are separated from the carding drum, such known apparatuses cannot be used for the production of uniform nonwoven webs at a relatively high fiber rate because an increase of the number of fibers which are to be separated from the carding drum per unit of time will increase the tendency of said fibers to form knots and this will be undesirable particularly in nonwoven webs which are light in weight. Besides, the length of the flight path for the fibers from the region in which they separate from the carding drum and the region in which they impinge on the collecting surface extending below the carding drum will necessarily depend on the diameter of the carding drum so that the entraining air must flow over relatively long distances particularly if the working widths are large so that the carding drums must be relatively large in diameter for ensuring the required strength. But such long flow paths for the entraining air will also increase the tendency to form knots.
In order to avoid those disadvantages which relate to the separation of the fibers from the carding drum it is possible to decrease the fiber density of the stream of fibers flying from the carding drum. From U.S. Pat. No. 4,583,267 it is known that for that purpose a plurality of closely spaced apart, consecutive carding drums may be provided so that each succeeding carding drum acts like a worker roller to comb out the fibrous material which has been fed by the next preceding carding drum. In that case only part of the fibrous covering on the next preceding carding drum is ejected through the nip between the carding drums onto the collecting surface and the fibrous covering is thus divided into a plurality of streams of fibers, which consecutively fly from respective carding drums and are deposited on a collecting surface, on which a vacuum is applied. That practice will not only ensure a substantially undisturbed transfer of the individual fibers from each carding drum to the collecting surface because the density of the fibers in the streams of fibers is limited, but will also ensure an equalization if irregularities occur in the distribution of fibers. The nonwoven web is built up on the collecting surface from the several streams of fibers, which consecutively impinge on the collecting surface at locations which succeed each other in the direction of travel of the collecting surface. But that desirable formation of the nonwoven web requires a higher structural expenditure because a plurality of carding drums must be arranged one behind the other and irregularities will inevitably occur as a part of the fibrous material is taken over by a succeeding carding drum and requires an equalization by additional pairs of worker and clearer rollers. Besides, the distance from the nip between two consecutive carding drums to the collecting surface will depend on the drum diameter and the use of drums which are larger in diameter will increase the tendency to form knots.